Delphi Retrieving updated TDataSet data in a background thread

[Lomanu4]

Remarks This FireDAC example, and the others I'm planning to submit, will avoid the use of native calls to asynchronously open the dataset. Examples FireDAC example The code sample below shows one way to retrieve records from an MSSql Server in a background thread using FireDAC. Tested for Delphi 10 Seattle As written: The thread retrieves data using its own TFDConnection and TFDQuery and transfers the data to the form's FDQuery in a call to Sychronize(). • The Execute retrieves the data only once. It could be altered to run the query repeatedly in response to a message posted from the VCL thread.

type
 TForm1 = class;
 TFDQueryThread = class(TThread)
 private
 FConnection: TFDConnection;
 FQuery: TFDQuery;
 FForm: TForm1;
 published
 constructor Create(AForm : TForm1);
 destructor Destroy; override;
 procedure Execute; override;
 procedure TransferData;
 property Query : TFDQuery read FQuery;
 property Connection : TFDConnection read FConnection;
 property Form : TForm1 read FForm;
 end;
 TForm1 = class(TForm)
 FDConnection1: TFDConnection;
 FDQuery1: TFDQuery;
 DataSource1: TDataSource;
 DBGrid1: TDBGrid;
 DBNavigator1: TDBNavigator;
 Button1: TButton;
 procedure FormDestroy(Sender: TObject);
 procedure Button1Click(Sender: TObject);
 procedure FormCreate(Sender: TObject);
 private
 public
 QueryThread : TFDQueryThread;
 end;
 var
 Form1: TForm1;
 implementation
 {$R *.dfm}
 { TFDQueryThread }
 constructor TFDQueryThread.Create(AForm : TForm1);
 begin
 inherited Create(True);
 FreeOnTerminate := False;
 FForm := AForm;
 FConnection := TFDConnection.Create(Nil);
 FConnection.Params.Assign(Form.FDConnection1.Params);
 FConnection.LoginPrompt := False;
 FQuery := TFDQuery.Create(Nil);
 FQuery.Connection := Connection;
 FQuery.SQL.Text := Form.FDQuery1.SQL.Text;
 end;
 destructor TFDQueryThread.Destroy;
 begin
 FQuery.Free;
 FConnection.Free;
 inherited;
 end;
 procedure TFDQueryThread.Execute;
 begin
 Query.Open;
 Synchronize(TransferData);
 end;
 procedure TFDQueryThread.TransferData;
 begin
 Form.FDQuery1.DisableControls;
 try
 if Form.FDQuery1.Active then
 Form.FDQuery1.Close;
 Form.FDQuery1.Data := Query.Data;
 finally
 Form.FDQuery1.EnableControls;
 end;
 end;
 procedure TForm1.FormDestroy(Sender: TObject);
 begin
 QueryThread.Free;
 end;
 procedure TForm1.Button1Click(Sender: TObject);
 begin
 if not QueryThread.Finished then
 QueryThread.Start
 else
 ShowMessage('Thread already executed!');
 end;
 procedure TForm1.FormCreate(Sender: TObject);
 begin
 FDQuery1.Open;
 QueryThread := TFDQueryThread.Create(Self);
 end;
 end.
Read Retrieving updated TDataSet data in a background thread online